Hot-curing epoxy resin adhesives have quite a long history of use as adhesives in bodyshell construction, and also in reinforcement elements or structural foams.
Known hot-curing epoxy resin adhesives are liquid, or at least paste-like, at room temperature, particularly where impact-resistant epoxy resin adhesives are involved. This can be disadvantageous when the composition has been applied and was intended to be dimensionally stable in storage prior to hardening. An additional disadvantage, alongside the specific disadvantage of change of shape during storage in the unhardened state, can be that mouldings here are also highly susceptible to dust problems, and this in turn can be attended by disadvantages in handling and in the adhesion of these mouldings. There is therefore great demand for solid-state hot-curing epoxy resin compositions which have an adhesion-free surface at room temperature.
There are known reinforcement elements which comprise a hot-curing epoxy resin composition which on exposure to heat give structural foam; an example has the trademark SikaReinforcer®. U.S. Pat. No. 6,387,470 B1 discloses by way of example a hot-curing, foamable sealing composition with a mixture of liquid epoxy resin and solid epoxy resin in the presence of from 5 to 20% by weight of a thermoplastic, such as polystyrene, and from 20 to 30% by weight of a thermoplastic elastomer, such as SBS block copolymer. However, the high proportion of SBS block copolymer can markedly impair the mechanical properties of compositions of this type, such as the glass transition temperature, and adhesion properties.